Model Citation II 550; Defog Blower

Model Citation II 550; Defog Blower

During descent after a 3-hour flight, the crew smelled exhaust-type fumes passing through 9,000 feet.

The crew turned the temperature control to “full cold,” and the smell disappeared. When the aircraft was level at 4,000 feet on the downwind leg, the crew selected increased heat on the temperature controller.

The fumes returned after a very short period of time, and the cockpit started filling with smoke. The crew donned oxygen masks, deployed passenger oxygen masks, and dumped pressurization. After turning the temperature control to “full cold,” the cockpit remained clear of any smoke.